When the board of supervisors determines on its own action to proceed to the establishment of a highway drainage district, it shall do so by the adoption of a resolution of necessity to be placed upon its records, in which it shall describe in a general way the portion of any highway or highways to be included in such district, together with the description of abutting or adjacent land and railroad rights-of-way to be included in such district and made subject to assessment for such improvement.
Iowa Code § 468.337
89 Acts, ch 126, §2